The present invention relates generally to mechanisms used for load compensating a door or hatch, and more particularly to a method and an apparatus for load compensating doors and hatches, including trunks and tailgates of automobiles.
Most of today's cars, trucks, vans, sport utility vehicles, etc., have doors or hatches such as trunks, hatchbacks, tailgates, or the like. These doors or hatches are very convenient in that accessibility to the inside of the vehicle is greatly enhanced. These doors and hatches are often quite large, therefore, they are often quite heavy.
To accommodate for the weight of the door or hatch, auto makers often put some sort of compensating device on the door or hatch to make the opening or lifting of it easier. Such compensating devices are known to include gas or mechanical springs and hydraulic struts.
Generally, a gas spring is a cylinder, sealed on both ends, which contains a shaft connected to a piston within the cylinder and extending out one end of the cylinder. Nitrogen, or an equivalent gas, is placed in the cylinder. The pressure created by the nitrogen applies force to the piston and causes the shaft to be extended. The amount of nitrogen placed in the cylinder can be varied to compensate for the weight of the door or hatch that is being supported. However, when a person closes the door or hatch, the force exerted on the piston by the nitrogen must be overcome in order to force the shaft back into the cylinder. Hence, the gas cylinder aids the opening of the door by load compensating the weight of the door or hatch during opening, but hinders the closing of the door or hatch by requiring more force to close it.
Similar to gas springs, hydraulic struts are comprised of a cylinder with a shaft attached to a piston. However, hydraulic struts utilize pressurized water, or similar liquid, to provide the force necessary for load compensating the weight of the door or hatch.
Additionally, hydraulic struts can be adapted to remove the excessive closing forces associated with gas springs. To accomplish this, the hydraulic strut is fitted with a mechanism providing override capability. Such an override mechanism puts a back pressure on the hydraulic system. This allows the door or hatch to be closed easily without the requirement of overcoming the load compensating forces of the hydraulic strut.
However, hydraulic struts are complicated systems. They are expensive to build and require power sources, such as special fluid pumps or the like, which are not typically present on the vehicle. In addition, adding override capability to a hydraulic strut is difficult to do, for a control must be used to sense when the door or hatch is being closed and thus applying a back pressure.
What is needed therefore is a method and an apparatus for load compensating doors or hatches for: (1) assisting in the opening of the door or hatch, (2) counterbalancing the door or hatch to keep it open, (3) easily overriding the load compensation forces for closing the door or hatch, and (4) utilizing a power source already present on a typical vehicle.